cpus.c: Drop unnecessary set_cpu_log()

cpus.c: Drop unnecessary set_cpu_log()

The set_cpu_log() function in cpus.c is a fairly simple wrapper
which is only called from one location. Just inline the code
into vl.c, since there is no need to indirect it via cpus.c
and the handling of the error case is more appropriate to vl.c.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Andreas Färber <afaerber@suse.de>
Signed-off-by: Blue Swirl <blauwirbel@gmail.com>